Cylinder liner and method for producing same

ABSTRACT

Disclosed is a cylinder liner having a high bonding strength to a cylinder block. Further disclosed is a method for producing the same. The cylinder liner uses a silicon-aluminum alloy as a material; a plurality of protrusions are formed on the external surface thereof; and the protrusions each contain a pillar section extending from the external surface, and a head section formed at the end of the pillar section.

This application is a divisional application of U.S. application Ser.No. 13/579,603, filed Aug. 17, 2012, which is a 371 application ofInternational Application PCT/JP2011/054759, filed on Mar. 2, 2011,which claims benefit to Japanese Application 2010-060795, filed Mar. 17,2010, the entire contents of which are incorporated herein by referencein their entireties.

TECHNICAL FIELD

The present invention relates to a cylinder liner and a method forproducing the same.

BACKGROUND ART

A cylinder block for use in automobile engines and the like comprises aplurality of cylinder bores inside each of which a piston slides. Here,a problem arises such that the inner surfaces of the cylinder bores areabraded due to the sliding of the pistons. In order to solve thisproblem, a cylinder block in which abrasion resistance is secured bycasting the entire cylinder block thereof from a high silicon-aluminumalloy such as A390 is proposed. However, a cylinder block formed of A390is very hard, making it difficult to process after casting. To solvethis problem, a cylinder block with cylinder liners provided in thecylinder bores is proposed (Patent Literature 1). This cylinder blockhas a structure wherein only the cylinder liners are formed of a highsilicon-aluminum alloy, and the remainder thereof is formed of analuminum alloy that does not contain silicon. Therefore, this cylinderblock is advantageous in that it can achieve a high abrasion resistanceon the piston-sliding surface, and, at the same time, is easilyprocessed after casting.

CITATION LIST Patent Literature

-   PTL 1: Japanese Unexamined Patent Publication No. 2002-504435

SUMMARY OF INVENTION Technical Problem

The cylinder liner for the cylinder block described above comprisesrecessions and protrusions on the external surface and is fixed in thecylinder bores by being cast into an aluminum alloy. However, such acylinder liner has a drawback in that it has insufficient bondingstrength with the cylinder block.

An object of the present invention is to provide a cylinder liner havinga high bonding strength with a cylinder block, and a production methodfor the same.

Solution to Problem

The present inventors conducted extensive research in order to achievethe above object and found that the bonding strength between a cylinderliner and a cylinder block depends on the shapes of the recessions andprotrusions, in particular the protrusions of the external surface ofthe cylinder liner. The present invention has been accomplished based onthis finding. More specifically, the cylinder liner of the presentinvention uses a silicon-aluminum alloy as the material, and comprises aplurality of protrusions formed on the external surface thereof, whereineach of the protrusions comprises a pillar section extending from theexternal surface, and a head section formed on the end of the pillarsection.

In the cylinder liner, each of the protrusions on the external surfacehas a constricted portion formed by a head section and a pillar section.Therefore, if this cylinder liner is united with a cylinder block byinserting it in an aluminum alloy or like metal by employinglow-pressure casting, die casting or the like, the cylinder liner andthe cylinder block can be firmly united because the molten metal cansecurely enter the constricted portions of the protrusions. Note thatthe concept of the cylinder liner of the present invention includes notonly those formed only of a silicon-aluminum alloy but also those formedof a material containing other components in addition to asilicon-aluminum alloy.

In the cylinder liner, the ratio of the distance from the externalsurface to the end surface of the head section to the distance from theexternal surface to the minimum diameter portion of the pillar sectionis preferably 2 to 80:1.

It is also possible to connect a plurality of the cylinder liners toform a cylinder liner-connected body.

The cylinder liner can be produced by, for example, using a moldcomprising a plurality of slides having recessions formed in theinternal surfaces thereof and a core. More specifically, a particulatemold release agent is adhered to the edge portions of the recessions inthe slides, and a molten silicon-aluminum alloy is flowed into thecavity and the recessions under the condition described above, therebycasting a cylinder liner-intermediate. Protrusions are formed on theexternal surface of the cylinder liner-intermediate. A mold releaseagent enters the root portion of each protrusion. Thereafter, thecylinder liner-intermediate is taken out from the mold and the moldrelease agent adhered to the surface of the cylinder liner-intermediateis removed, obtaining a cylinder liner having protrusions with each ofwhich root portion is constricted. In this specification, the termcavity refers to the space in which a cylinder liner-intermediate ismolded.

In the above production method, the particulate mold release agent maybe adhered to the edge portions of each recession of the mold, forexample, by charging the mold release agent by a corona discharge. Inthis method, because a large amount of charged mold release agentadheres to the edge portions of each recession where the electricallines of force concentrate, a large amount of mold release agent can bemade to enter the root portions of protrusions of the cylinderliner-intermediate, forming a deep constriction at each root portion ofprotrusion of the cylinder liner-intermediate.

In the above production method, the external surface of the particulatemold release agent may be covered with a material containing an organiccomponent. In this method, when the mold release agent is adhered to theedge portions of each recession, because the organic component on theexternal surface of the mold release agent melts due to the heat of themold, the mold release agent can firmly adhere to the edge portions ofeach recession. Furthermore, because particles of mold release agentwhose external surfaces are molten adhere to each other, the moldrelease agent can be laminated in the edge portions of the recession.This allows a larger amount of the mold release agent to enter the rootportion of each protrusion of the cylinder liner-intermediate, forming adeep constriction in the root portion of the protrusion of the cylinderliner-intermediate.

In the above production method, air in the cavity may be discharged fromoutlets each formed in the bottom of each recession in the slide. Morepreferably, air in the cavity is actively removed by suction through theoutlets. According to this method, the cavity can be decompressed bydischarging air therefrom; therefore, the silicon-aluminum alloy can beeffectively flown into the recessions. This allows the protrusions ofthe cylinder liner to be formed in a reliable manner.

In the above production method, each cavity delimited by the mold mayhave a form such that two or more tubes are connected. This makes itpossible to produce a cylinder liner-connected body applicable to acylinder block for a multiple-cylinder engine. As a result, productiontime can be reduced and advantages can be gained in terms of productioncost.

It is also possible to produce a cylinder liner by using a productionapparatus comprising the mold as described above, and an adhering meansfor adhering a mold release agent to the edge portions of recessions.

In the above production apparatus, the adhering means may be such thatthe mold release agent is electrically charged by a corona discharge.

The production apparatus may further comprise a means for casting acylinder liner-intermediate using a molten silicon-aluminum alloy; ameans for releasing the cylinder liner-intermediate that was formed bythe casting means from the mold; a means for removing the mold releaseagent from the cylinder liner-intermediate; etc. Examples of the castingmeans include gravity casting, low-pressure casting, die casting and thelike. The means for releasing the cylinder liner-intermediate may besuch that the slides are shifted to release the cylinderliner-intermediate, or when a core is used, the cylinderliner-intermediate or the core may be pulled or pushed out. Examples ofthe removing means include the use of a brush, immersion in a solventthat can dissolve the organic component, ultrasonic cleaning, etc.

Advantageous Effects of Invention

The present invention can increase the bonding strength between thecylinder liner and the cylinder block.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically illustrating the cylinderliner and cylinder block according to the embodiment described above.

FIG. 2 is a partial front sectional view of the cylinder liner accordingto the embodiment described above.

FIG. 3 is a plan view schematically illustrating the mold and coreaccording to the embodiment described above.

FIG. 4 is a partial front sectional view schematically illustrating themold according to the embodiment described above.

FIG. 5 is a partial front sectional view schematically illustrating themethod for producing a cylinder liner according to the embodimentdescribed above.

FIG. 6 is a cross-sectional photograph showing a part of the cylinderliner according to the embodiment described above.

FIG. 7 is a plan view schematically illustrating the mold and coreaccording to a modified example of the embodiment described above.

DESCRIPTION OF EMBODIMENTS

One embodiment of the cylinder liner of the present invention, aproduction apparatus thereof and a production method thereof areexplained in detail below with reference to the attached drawings.

First, the cylinder liner 1 according to the present embodiment isexplained below.

As shown in FIG. 1, a cylinder liner 1 is used by being inserted in acylinder bore 21 of a cylinder block 2. The cylinder liner 1 is made ofa silicon-aluminum alloy, and comprises a plurality of protrusions 12 onthe external surface thereof as shown in FIG. 2. The protrusion 12comprises a pillar section 13 and a head section 14 whose diameter islarger than that of the pillar section 13. Note that, in the protrusion12 of the cylinder liner 1, the difference between the diameter D1 ofthe pillar section 13 and the diameter D2 of the head section 14 ispreferably 2 μm or more, wherein D1 is preferably 300 μm or more and D2is preferably 302 μm or more. The height H1 of the pillar section 13 ispreferably 50 to 1,000 μm, the height H2 of the head section 14 ispreferably 50 to 2,000 μm, and the ratio of H1 to H2 is preferably 1:1to 40 (H1:H2=1:1-40), more preferably H1:H2=1:1 provided that H1≦H2.FIG. 6 shows one example of the shape of the protrusion formed on theexternal surface of the cylinder liner.

The apparatus for producing the cylinder liner 1 described above isexplained below.

As shown in FIGS. 3 to 5, the production apparatus is provided with amold 3 and an adhering means 6 for adhering a particulate mold releaseagent 5 to the mold 3.

As shown in FIG. 3, the mold 3 delimits the cavity 7, and the cavity 7is used for casting a cylinder liner-intermediate 8 described below. Themold 3 is composed of a first to fourth slides 3 a to 3 d that areopenable/closeable in the diagonal direction (in the direction shown bythe arrows in FIG. 3) and a core 4. A plurality of recessions 32 areformed on the inner surface 31 in each of the first to fourth slides 3 ato 3 d. The recessions 32 are to form protrusions 82 on the externalsurface of the cylinder liner-intermediate 8, and extend along thediagonal direction of the first to fourth slides 3 a to 3 d. As shown inFIG. 4, an outlet 33 for discharging air from the cavity 7 is formed inthe bottom of each recession 32. The core 4 is made of metal and locatedin the center of the first to fourth slides 3 a to 3 d in order to diecast the cylinder liner-intermediate 8.

As shown in FIG. 5(a), the adhering means 6 is designed so as to sprayor blow the particulate mold release agent 5 onto the first to fourthslides 3 a to 3 d and the core 4 by passing it through the passage 61along the airflow. The adhering means 6 also electrifies the moldrelease agent 5 by means of the needle electrode 62 provided on the tipof the passage 61 and an external power source 63 located outside of thepassage 61. More specifically, electric power from the external powersource 63 is supplied to a high-voltage generator (not shown) togenerate a high voltage, and the high voltage thus generated is appliedto the needle electrode 62. This generates a corona discharge to formcorona ions around the needle electrode 62. Due to the adhesion of thecorona ions to the mold release agent 5 that passed through the passage61, the mold release agent 5 becomes charged. Examples of the adheringmeans 6 include commercially available corona powder coating guns suchas the MATSUO X-1a (manufactured by Matsuo Industry Corporation).

The mold release agent 5 preferably has a particle diameter of 1 to 100μm, and more preferably 5 to 50 μm. Furthermore, the mold release agent5 preferably has a structure wherein the central portion thereof isformed of a material containing an inorganic component, and the externalsurface thereof is covered with a material containing an organiccomponent. Examples of the organic component includepolytetrafluoroethylene, polyvinyl chloride, polyethylene,polypropylene, carnauba wax, acrylic resin, epoxy resin, polystyrene,polyurethane, nylon 6, nylon 66, nylon 11, nylon 12, cellulose, fattyacid, higher alcohol, metal soap, fatty acid amide, fatty acid ester,alkali salt of fatty acid and the like. Examples of the inorganiccomponent include talc, mica, black lead, diamond, molybdenum disulfide,boron nitride, alumina, silica, titania, zinc oxide, iron oxide,diatomaceous earth, zeolite and the like. The mold release agent 5 usedin the present embodiment is obtained by coating the surface of NanoTek® SiO2 (a commercially available material manufactured by C.I. KaseiCo., Ltd.) with Alflow® H-50TF (manufactured by NOF Corporation).

The method for producing a cylinder liner using the production apparatusdescribed above is explained below with reference to mainly FIG. 5. Notethat FIG. 5 illustrates only the first slide 3 a; however, the second tofourth slides 3 b to 3 d follow the same procedure as the first slide 3a.

First, as shown in FIG. 5(a), the first slide 3 a is heated and groundedusing a ground wire 9. The temperature of the first slide 3 a ispreferably higher than the melting point or softening point of theorganic component coating the mold release agent 5, and is specifically100 to 300° C. Subsequently, with the mold 3 open, a high voltage isapplied to the needle electrode 62 by the adhering means 6 to electrifythe particulate mold release agent 5, and the electrified mold releaseagent 5 is sprayed toward the internal surface 31 of the first slide 3a. Here, the electrified mold release agent 5 adheres to the entireinternal surface 31 except for the inside of the recessions 32. Inparticular, a large amount of the electrified mold release agent 5adheres to the edge portions 34 of the recessions 32 to which electricallines of force concentrate. Thereafter, while maintaining the core 4 atroom temperature (25° C.), the mold release agent 5 is also adhered tothe external surface 41 of the core 4 by the adhering means 6 (FIG.5(b)). The mold release agent 5 is preferably adhered to the first tofourth slides 3 a to 3 d and core 4 each time that casting is performed.The voltage applied to the needle electrode 62 is preferably 20 to 100kV. The air pressure when the mold release agent 5 is sprayed onto thefirst slide 3 a and core 4 is not particularly limited and may besuitably selected within a range that is sufficient to allow the moldrelease agent 5 to reach the first slide 3 a and to be sufficientlyelectrified when the mold release agent 5 passes near the needleelectrode 62. Specifically, the air pressure is 0.01 to 0.5 MPa.

After reducing the pressure in the cavity 7 by sucking the air from thecavity 7 via outlets 33 of the first slide 3 a, a cylinderliner-intermediate 8 is cast in the cavity 7 using a moltensilicon-aluminum alloy by gravity casting, low-pressure casting, diecasting, or the like (FIG. 5(c)). Because the pressure of the cavity 7is reduced, the silicon-aluminum alloy is reliably flowed also into therecessions 32. The temperature of the silicon-aluminum alloy ispreferably 700 to 800° C. The silicon-aluminum alloy has a siliconcontent of preferably 13 to 23% and more preferably 14 to 18%. In thepresent embodiment, high silicon-aluminum alloy A390 is used.

Subsequently, the first to fourth slides 3 a to 3 d are opened indiagonal directions (the directions shown by the arrows in FIG. 3), andthe cylinder liner-intermediate 8 is pulled in the axial direction totake out the cylinder liner-intermediate 8 from the first to fourthslides 3 a to 3 d and core 4. The mold release agent 5 is adhered to theentire surface of the cylinder liner-intermediate 8 taken out, and aparticularly large amount of the mold release agent 5 penetrates intothe root portions 83 of the protrusions 82 formed on the externalsurface 81 (FIG. 5(d)).

Next, the mold release agent 5 is removed from the surface of thecylinder liner-intermediate 8 by using a brush. The cylinderliner-intermediate 8 is then immersed in a paraffin-based mineral oil(solvent) to dissolve the organic component on the external surface ofthe mold release agent 5. After applying ultrasonic cleaning to thecylinder liner-intermediate 8, the cylinder liner-intermediate 8 iswashed with petroleum ether. This allows the mold release agent 5 thatadhered to the entire surface of the cylinder liner-intermediate 8 andthe mold release agent 5 that penetrated into the root portions 83 ofthe cylinder liner-intermediate 8 to be removed, obtaining a cylinderliner 1 comprising protrusions 12 formed on its external surface 11.Here, each protrusion 12 is composed of a pillar section 13 and a headsection 14, wherein the pillar section 13 has a diameter smaller thanthat of the head section 14 (FIG. 5(e)). The cylinder liner 1 thusproduced is placed into a die for a cylinder block (not shown). Bycasting it in a molten aluminum alloy by means of low-pressure castingor die casting, a cylinder block 2 having cylinder bores 21 into each ofwhich a cylinder liner 1 is fixed is formed (FIG. 1). Thereafter, theinternal surface of the cylinder liner 1 is subjected to a boringprocess, honing, and edging to obtain a finished product.

As described above, the cylinder liner 1 according to the presentembodiment is structured so that it comprises protrusions 12 formed onthe external surface 11, wherein the diameter D1 of the pillar section13 is smaller than the diameter D2 of the head section 14 so that theroot portion of each protrusion 12 becomes constricted. Therefore, whena silicon-aluminum alloy is welded to the cylinder liner 1 to unify thecylinder liner 1 with the cylinder block 2, the silicon-aluminum alloyeffectively enters the constricted portion of each protrusion 12, sothat the cylinder liner 1 and the cylinder block 2 can be securelyunited to each other. As a result, machining can be applied to the innersurface of the cylinder liner 1 without shifting, finishing to a highlyprecise inner surface. This also improves the performance of the enginein actual operation. Furthermore, in the present embodiment, byelectrifying the mold release agent 5 by a corona discharge, aparticularly large amount of the mold release agent 5 can be adhered toedge portions 34 of recessions 32 of the mold 3. This makes it possibleto cast a cylinder liner-intermediate 8 having a larger amount of themold release agent 5 penetrated into the root portion 83 of eachprotrusion 82 and to form a deep constriction at the root portion ofeach protrusion 82 of the cylinder liner 1. Furthermore, in the presentembodiment, because the silicon-aluminum alloy is flowed into the cavity7 while keeping the core 4 at room temperature, the silicon-aluminumalloy is rapidly cooled inner side the cavity 7 by the core 4, and alarge amount of silicon crystal particles can be deposited. This causesmany silicon crystal particles to exist on the internal surface 15 ofthe cylinder liner 1, reliably obtaining a high abrasion resistance.

One embodiment of the present invention is explained above; however, thescope of the present invention is not limited to this, and variousmodifications may be made as long as they do not depart from theintention of the present invention. For example, in the aboveembodiment, the mold release agent 5 is adhered to the entire internalsurface of the mold 3; however, all that's necessary is that the moldrelease agent is adhered at least to the edge portions of recessions,and, for example, the mold release agent may be adhered to a portionother than the edge portions in a striped pattern. Note that it ispreferable that the mold release agent be adhered to the internalsurface (excluding the recessions) of the mold so as to prevent thesilicon-aluminum alloy from solidifying before flowing into therecessions.

In the above embodiment, the mold release agent 5 is electrified by acorona discharge to adhere it to the mold 3 and core 4. However, as longas the mold release agent can be adhered at least to the edge portionsof recessions, the method is not limited to the above, and, for example,the mold release agent may be simply applied to the mold withoutelectrifying.

In the above embodiment, only the root portion is constricted in eachprotrusion 12 of the cylinder liner 1; however, the structure thereof isnot limited to this as long as the root portion of each protrusion canbe made constricted, and, for example, at least one or moreconstrictions may be formed in the head section of the protrusion.

Furthermore, in the above embodiment, the head section 14 of theprotrusion 12 has a pillar-like shape with an almost uniform diameter.However, the shape of the head section 14 is not limited to this and maybe formed into various shapes such as spherical, conical, pyramidal andthe like.

In the above embodiment, the mold release agent 5 is removed from thecylinder liner-intermediate 8, after removing the mold release agent 5that has adhered to the surface of the cylinder liner-intermediate 8 byusing a brush, by immersing the cylinder liner-intermediate 8 in asolvent to dissolve the external surface of the mold release agent 5,and further performing ultrasonic cleaning. However, any method can beemployed as long as the mold release agent can be removed from thecylinder liner-intermediate. For example, the mold release agent may beremoved by at least one means selected from removal using a brush,immersion in a solvent, and performing ultrasonic cleaning. When themold release agent 5 is removed by only immersion in a solvent, theexternal surface of the mold release agent 5 is preferably covered withan organic component.

In the above embodiment, a paraffin-based mineral oil is used as asolvent. However, the solvent is not limited to this as long as it candissolve or disperse the organic component, and, for example, anaromatic solvent, water, a mixture of water and surfactant, an acid oralkali aqueous solution and the like may be used.

In the above embodiment, the cylinder liner is produced using a mold 3comprising the first to fourth slides 3 a to 3 d. However, the mold isnot limited to this as long as a cylinder liner-intermediate havingprotrusions on the external surface can be taken out, and a 6 or 8-piecesplit mold may be used.

In the above embodiment, the core 4 is maintained at room temperature;however, the temperature of the core 4 is not limited to this as long asit is lower than that of the plurality of slides.

In the above embodiment, the core 4 is metallic; however, the materialfor the core 4 is not limited to metal as long as it can die cast thecenter of the cylinder liner-intermediate, and the core 4 may be made ofsand, ceramics and the like. Even when a core made of sand or ceramicsis used, when its temperature is maintained lower than that of theplurality of slides, many silicon crystal particles can be formed insidethe cylinder liner.

In the above embodiment, air in the cavity 7 is sucked through theoutlets 33 of the mold 3; however, possible embodiments are not limitedto this, and the air in the cavity 7 is not necessarily sucked out. Inthis case, the pressure of the cavity can be reduced by naturallyreleasing the air through the outlets.

Furthermore, a single cylinder liner 1 is produced in the aboveembodiment; however, possible embodiments are not limited to this, and acylinder liner-connected body in which a plurality of cylinder linersare connected may be produced. In this case, for example, as shown inFIG. 7, a cylinder liner-connected body can be produced by aligning aplurality of sets of mold 3 that are similar to that used in the aboveembodiment, and arranging fifth and sixth slides 30 a, 30 b between themolds.

The plurality of protrusions formed on the cylinder liner do notnecessarily have to have the same shape as that in the embodimentdescribed above as long as a strong adhesion between the cylinder linerand the cylinder block can be secured. The protrusions may include, forexample, those having no constricted portion; those having a ratio ofother than 2 to 80:1 for the distance from the cylinder liner externalsurface to the end surface of the head section to the distance from thecylinder liner external surface to the minimum diameter portion of thepillar section; etc.

EXPLANATION OF NUMERICAL SYMBOLS

-   1 cylinder liner-   2 cylinder block-   12 protrusion-   13 pillar section-   14 head section-   3 mold-   3 a-3 d first to fourth slides (a plurality of slides)-   32 recession-   34 edge portion-   33 outlet-   4 core-   5 mold release agent-   6 adhering means-   7 cavity-   8 cylinder liner-intermediate

1-3. (canceled)
 4. A method for producing a cylinder liner comprising:preparing a mold having a plurality of slides and a core fordelimitating a cavity, the plurality of slides having recessions in thesurface facing the cavity and being movable along the direction in whichthe recessions extend; adhering a particulate mold release agent to edgeportions of the recessions; casting a cylinder liner-intermediate byflowing a silicon-aluminum alloy into the cavity and the recessions;taking the cylinder liner-intermediate out from the mold; and removingthe mold release agent from the cylinder liner-intermediate.
 5. Themethod according to claim 4, wherein the mold release agent iselectrified by a corona discharge.
 6. The method according to claim 4,wherein the external surface of the mold release agent is covered with amaterial containing an organic component.
 7. The method according toclaim 4, wherein the cavity has a shape in which a plurality of tubesare interlinked.
 8. The method according to claim 4, wherein air in thecavity is discharged from an outlet formed in the bottom of eachrecession formed in the plurality of slides.
 9. An apparatus forproducing a cylinder liner comprising: a mold having a plurality ofslides and a core for delimiting a cavity, the plurality of slideshaving recessions in the surface facing the cavity and being movablealong the direction in which the recessions extend; and an adheringmeans for adhering a particulate mold release agent to edge portions ofthe recessions.
 10. The apparatus for producing a cylinder lineraccording to claim 9, wherein the adhering means electrifies the moldrelease agent by a corona discharge.
 11. The method according to claim5, wherein the external surface of the mold release agent is coveredwith a material containing an organic component.
 12. The methodaccording to claim 5, wherein the cavity has a shape in which aplurality of tubes are interlinked.
 13. The method according to claim 6,wherein the cavity has a shape in which a plurality of tubes areinterlinked.
 14. The method according to claim 5, wherein air in thecavity is discharged from an outlet formed in the bottom of eachrecession formed in the plurality of slides.
 15. The method according toclaim 6, wherein air in the cavity is discharged from an outlet formedin the bottom of each recession formed in the plurality of slides. 16.The method according to claim 7, wherein air in the cavity is dischargedfrom an outlet formed in the bottom of each recession formed in theplurality of slides.